A received signal strength indicator (RSSI) is used to measure the strength of signals received by a radio receiver. Typically, these signals include the wanted signal and unwanted other signals (sometimes called blockers or interferers). Generally, the receiver operates best when the wanted signal is at a usefully high level, thus it is advantageous to turn the gain up. However, this may cause the unwanted signals to overload the receiver and cause it to not receive the wanted signal properly. The RSSI provides a coarse view of whether the receiver can turn its gain up, or not. If it cannot, other strategies may be open to it—for example, additional filters, or asking the wanted transmitter to turn its amplitude up.
RSSI detectors are often configured to output a direct current or voltage (DC), because this uses fewer resources to measure and evaluate than an alternating current or voltage (AC). Thus they often comprise a rectification circuit to convert the incoming signal from an AC signal to a DC one. FIG. 1 illustrates a known rectification circuit of an RSSI detector. A complementary AC signal is input on lines 101a, 101b, and a DC reference level is input on line 102. A current source 105 provides operating current and capacitor 106 low pass filters current into load 107, making the voltage primarily change with the DC output. For sufficiently large signals devices 103a, 103b provide a non-linear transfer function that has the effect of rectifying a fraction of the incoming signal.
The rectification circuit of FIG. 1, and other known circuits, provide effective rectification when operated at a high enough operating current, but as the current drops their speed becomes a problem, and their performance drops.
With increased market demand for lower power/longer battery life electronic devices, a lower power solution to providing an effective RSSI detector is needed.